System for compensating for differences in potential



Oct. 18, 1938. G. A. PULLIS SYSTEM FOR GOMPENSATING FOR DIFFERENCES INPOTENTIAL Filed June 12, 1937 h 5 a Hm RU. .N 0 R T 0 N W I I A H W m aP a. m W

Patented Oct. 18, 1938 UNITED STATES PATENT OFFICE SYSTEM FORCOMPENSATIN G FOR DIFFER- ENCES IN POTENTIAL George A. Pullis, Hoboken,N. J., assignor to Bell Telephone Laboratories,

Incorporated, New

-7 Claims.

This invention relates to what are known as duplex signaling systemscommonly used in telephone systems for direct current signaling overrelatively long lines.

Such a system is described in Patent 1,287,831 in which compensation fordifierences in earth potentials at the two terminals of the line iseffected by a compensating or third winding on the multiwinding linerelay at each terminal, which compensating windings are connected inseries between ground at each terminal over a separate line conductor.By this arrangement, differences in potential between the groundconnections at each terminal will cause current to flow through both ofthe compensating windings in series thereby maintaining the properbalance in the differential windings of the two relays.

Such an arrangement, however, does not compensate for voltagedifferences between the sig- 2O naling batteries at the two terminals ofthe line which may, at times, be sufiiciently great to ef- .fect theproper operation of the signaling relays which are, of necessity,adjusted to very close margins as regards their-operate and non-operatecurrents.

An object of the present invention, therefore, is to compensate not onlyfor differences in ground potentials at the two ends of such a system,but also to compensate for potential difier- 3O ences between thesignaling batteries at each end during the transmission of signals,particularly dial impulses.

A feature of the invention whereby the foregoing object is attainedresides in connecting each end of the compensating circuit to a point ina potentiometer supplied by the respective signaling batteries, thusapplying a predetermined fraction of the voltage of each battery to therespective ends of the compensating circuit L whereby any difierencewhich may exist between the signaling battery voltages at the two endsof the line, which might otherwise cause distortion and improperoperation of the signaling relays, will also cause a proportional flowof current in L5 the compensating winding of each relay in such adirection as to balance out such distortion effect.

The invention will be understood from the accompanying drawing whichshows two physical two-wire lines extending between distant sterminalsarranged to provide three signal transmission channels in eachdirection.

No attempt has been .made to show any particular system of signals otherthan to diagram- -matically indicate a signal transmitting means such asthe contacts of a pulsing device (dial) and a signal receiving devicesuch as a pulse relay per channel at each terminal, it being obviousthat any desired system of signal control can be employed both fortransmitting and receiving ,5

signals over the transmission channels herein provided.

A description of the invention follows: Between the terminals A and Bextend two physical twowire lines L and LI terminating at each end inany desired telephone or other equipment'not shown, as for example, intelephone switching apparatus shown in the before-mentioned BascomPatent 1,287,831.

For purposes of signaling between terminals, three two-way signalchannels areprovided comprising line conductor I of line L andconductors 3 and 4 of line 2 and multiwound polarized relays 5, t, l, 8,9 and Ill. Relays 5, 6, I, 8, 9 and I0 have three windings each, theupper windings being designated the line windings, the middle designatedthe biasing windings and the bottom designated the compensatingwindings.

Associated with each of the above relays is shown an auxiliary pulsereceiving relay I I I2,v I3, I4, I5 and I6, respectively, which iscaused to respond when its associated polarized relay is operated. Also,associated with each polarized relay are respective transmitting relaysand dial contacts I'i, I8, I9, 20,*2I, 22, 23, 24, 25, 26 and 21, 28,Under normal conditions relays I'I, I9, 2|, 23,25, and 2? are releasedand connect ground through the upper or line winding of their respectivepolarized relay to one of the line conductors, relay IT, for example,connecting ground through 5 limiting resistance 29, back contact ofrelay I'I, upper winding of relay 5 and impedance coil'30 to lineconductor I where it meetsground applied to the other end of this sameconductor over the back contact of relay 23 and upper winding of relay8.

If the ground potential is thesame at terminals -A and B, no currentflows in the line windings of relays 5 and 8 and these relays are notaffected.

It should be mentioned that although different I batteries are indicatedon the drawing for each signal channel at each terminal, all thebatteries indicated by the reference character B at terminal A are oneand the same battery at that terminal and those indicatedas B atterminal B are also one and. the same'battery forthat terminal. It, alsois assumed that batteryB at terminal A and battery B atterminal B arenor mally of the same voltage.

Relays I1, 23, I9, 25, etc. while in their normal condition also connectground to one end of the middle or biasing windings of the respectiverelays 5, 8, B, 9, etc., the other ends of which are connected through anetwork N1, N2, N3, N4, N5 or N6 to a point in a battery potentiometerarrangement P1, P2, P3, P4, P5 or F6, so chosen in practice as to beapproximately one-third the potential of the supply battery B or B. Inpractice, the values of the two resistance elements of potentiometers Pare of the high order of 1500 and 3000 ohms, thus reducing the currentdrain on the respective battery to a substantially negligible quantity.

Assuming relay H to be in its released condition, ground is connectedthrough resistance 29 to one end of the middle winding of relay 5, andas the other end is connected to the point 3| of potentiometer P1,current will therefore flow in this Winding in a direction, which ispredetermined by the connection of the two ends of the winding in thecircuit, to energize relay 5 in a non-operate direction thus maintainingthis relay'in a released condition.

When battery is connected to one end of a channel, for example, whendial contacts 18 are closed, thus causing relay I? to close itscontacts, battery B is substituted for the ground connection includingresistance 29, whereupon current flows in the opposite direction in themiddle or biasing winding of relay 5, which current flow tends tooperate this relay. However, under this condition current also flows inthe upper or line winding of relay 5 in a direction which opposes theoperating efiect of the current in the middle or biasing winding andtherefore the relay remains released.

At the other end of the channel, however, if

relay 23 remains released, current now flows in the line winding ofrelay 8 in a direction to cause it to operate,'which current overcomesthe nonoperate effect of the middle winding due to the direction of thecurrent flow therein and therefore relay 8 operates and closes a circuitto operate relay I4.

As before mentioned, the points, such as 3!, in the respectivepotentiometers are so chosen that the potential thereof is a certainpredetermined portion of the potential of the battery, in

this case one-third. Therefore, when relay H, for example,'is in itsnormal or released condition and ground is connected at its backcontact, current at one-third the potential of the battery B flows inthe middle winding of relay 5 in a non-operate direction and no currentflows in the upper or line winding, whereas when relay operates andbattery B is connected at its front contact, current at the fullpotential of the battery flows in the upper line winding in a nonoperatedirection and at two-thirds the potential of the battery B in the middleor biasing winding in an operate direction whereby the relay 5 is stillmaintained in a non-operate condition.

On the other hand, when relay 1'! is operated at terminal A and relay 23is released at terminal B, current at the full potential of the batteryB flows in the upper or line winding of relay 8 in an operate directionand at one-third the potential of battery B in a non-operate directionin the middle or biasing winding thus causing relay 8 to operate.

In the case of simultaneous signal transmission from each terminal overthe same channel, both relays l1 and 23',for example, are operatedthereby connecting battery to line conductor I at each terminal throughthe respective line windings of relays 5 and 8 and if batteries B and B'are assumed to be equal no current will flow in the line windings ofthese two relays and both will operate due to current flowing in anopposite direction in their biasing windings as previously described.

It will be noted from the drawing that line conductors I, 3 and 4 areutilized as signaling channels and that a connection at each terminaleartends from conductor 2 through the lower or compensating windings ofall three polarized relays in series to a point in a fourthpotentiometer GP or CF connected in shunt to the grounded signalbatteries B and B, respectively, which point is also the same proportionof the signal battery voltage as that of the point 3| of thepotentiometer P1, for example.

In the patent to Bascom 1,287,831, previously referred to, acompensating circuit is described which serially includes a lineconductor and a third winding on each of the signal relays, whichcircuit is connected to ground at each terminal of the line. Such acircuit arrangement is described as providing compensation for theeffect on the'signal or line winding of the multiwound relays R3, R3 bycurrent flowing in the trunk conductors L, L2 and L3 due. to adifference in the ground-potential between the two terminals of theline.

Bascoms system, however, has no provision for compensating for voltagevariations in the signaling batteries at each end of the line and suchcompensation is not necessary for the type of signaling disclosed in thepatent, i. e., supervisory signaling.

In the present arrangement, which provides for dialing in eitherdirection, it is necessary, for the proper functioning of the switchingequipment, that the line relays, i. e., relays 5, 8 and 6, 9, etc.,follow the received dial pulses within certain definite predeterminedlimits as otherwise failure in the operation of the switching equipmenttakes place To obtain this desired result,

the relays 5, 8, etc., are electrically polarized by current flowing inthe middle or bias winding.

"The direction and value of this bias current is fully described in thepreceding pages.

As mentioned above, the two batteries at the opposite terminals areassumed to be normally of 'tocontrol the switching equipment withoutfailure. If, however, in the absence of compensation for differences inbattery potential at the two ends of the line, a potential differenceoccurs,; i. e., let us assume for example that the normal voltage ofbatteries B and B is 45 bolts and that battery B becomes overcharged andits voltage rises to 51 volts, while battery B remains at its normalvalue, then a potential difference of 6* volts exists between batteriesB and B and the potential of point 3| of potentiometer B is 17 volts,whereas the corresponding point in potentiometer B is 15 volts. Now Whendial 18 at ter- 'minal A is transmitting pulses there will be a:

greater proportionate flow of current in the operate direction in theupper winding of relay 8 of terminal B, (i. e., current due to 51 volts)than in the non-operate direction in the middle winding of the samerelay (1. e., current due to 15 during which the relay is released areshorter than desired, which may affect the operation of the switchingequipment which requires a rather definite ratio between the closed andopen condition of the contact of the line relay 8.

On the other hand if the dial 24 at terminal B' is operated there willbe proportionally less current flowing in the operate direction in theupper winding of relay 5 (i. e., flux due to volts) than inthenon-operate direction in the middle or bias winding of the same relay(1. e., flux due to 17 volts) which will tend to cause re- .;ay 5 tooperate more slowly. When each pulse ends relay 5 will tend to releasemore rapidly than when it is energized by the normal flux and now theclosed interval of contacts of relay 5 is relatively shorter and theopen interval longer than normal which ratio may also affect theoperation of the switching equipment at that end of the line.

In the foregoing description, it has been assumed that no groundpotential difference exists between the. two ends of the line. Of courseif such a condition does exist such differences must be compensated forwhich can be done as shown in the Bascom patent, above refered to, byconnecting ground to the end of a compensating circuit including a thirdwinding on each of the two line relays 5 and 8, and a conductor 2 of theline, but this will not affect any compensation for the differencebetween the potentials of the two batteries.

In the foregoing it has been shown that in a system of the typedisclosed in the present application, a compensating circuit connectedto ground at both ends will not compensate for variations in the linebattery. This result can. however, be obtained by includinga fraction ofthe potential of each battery in the grounded compensating circuit shownin the drawing, i. e., in addition to the three potentiometers P1, P2,P3 of terminal A, and P4, P5 and P6 of terminal B, which are connectedin shunt to their respective batteries B and B, a fourth potentiometerGP or CF is connected in shunt to each battery (B or B) and byconnecting one end of the compensating circuit, to point 32 in thefourth potentiometer CP of terminal A and the other end to point 33 inthe potentiometer CP' of terminal B. It will be noted that each end ofthe compensating circuit is still connected to ground, which compensatesfor differences in ground potential between the two ends of the line, asin the Bascom arrangement, but also by including the battery at each endany increase or decrease from normal of either battery will also affecteach relay in the circuit in such a manner as to counteract theundesired effects caused by abnormal currents in the other two windingsof the same relay. For example, in the case before assumed, when batteryB is 51 volts and B 45 volts, with the compensating circuit connected asshown in the drawing, there will be a potential difference of 2 voltsbetween point 32 of potentiometer CP at terminal A and point 33 ofpotentiometer CP' at terminal B which will cause current to flow in thelower windings of relay 5 and'8 in. such a'direction as to increase theeffective-bias in relay8 to avalue which would be equal to that whichwould exist if the battery B had been 51 volts instead of 45 volts, andto decrease the effective bias in re1ay'5 to a value which would beequal to that which would exist if the "battery B had been 45 voltsinstead of 51 Volts. Therefore, it can be stated that regardlessof thevoltage at either end, that is for reasonable variation from normal, theeffective bias current at the terminal receivingthe dial pulses willalways be equal to a value which would existif the battery at thereceiving terminal were the same as that at the sending terminal.

What is claimed is:

1. In a duplex signaling system, a line, a grounded source of directcurrent and a multiwinding polarized relay at eachend thereof, a linewinding on each relay connected to one side of theline, a biasingwinding on each relay energized in a local circuit by a fraction of thepotential of the respective current source, a potentiometer in shunt ofeach source, and means for compensating for differences in thepotentials of the two earth points and also the two current sources,said means including a compensating win-ding on each relay connectedbetween the other side of the line. and a point in the respective.potentiometer.

2..In a duplex signaling system, a line, stations at each end thereof,multiwin-ding polarized signal relays at each station, direct currentsources of normally equal potential associated with each relay, a localbiasing circuit for each;-

relay including a winding thereof, means for applying a predeterminedproportion of the voltage of each source to the respective biasingcircuit, a potentiometer in shunt of each current source,-a signalingwinding on each relay connected to one side of the line, and acompensating winding on each relay included in a circuit from ground atone station through a portion of the respective potentiometer over theother conductor of the line to ground at the other station through anequivalent portion of the potentiometer at the station, saidpotentiometers associated with the compensating circuit being soarranged that the potential applied to either compensating winding isthe same as the potential normally applied to the respective biasingwinding.

3. In a duplex signaling system, a line, stations at each end thereof, agrounded source of signaling current at each station, said sources beingnormally of substantially equal potential but subject to independentvariations, multiwinding' polarized signal relays at each station, alocal biasing circuit for each relay including one winding thereof andmeans for applying a potential thereto comprising a potentiometer inbridge of the respective source, said potentiometers being so arrangedthat the potential applied to each biasing winding is the sameproportion of the voltageof the associated source, switching means ateach station normally connecting ground: through a second winding of therespective relay at each station through a portion of the respectivesecond potentiometer, the point of connection to each compensatingpotentiometer delivering the same proportion of the voltage of theassociated source as the normal potential applied to the correspondingbiasing winding.

4. In a duplex signaling system, a line, equal potential groundedsources of signaling current at each end thereof, said grounds andcurrent sources being independently subject to variations of potential,a multiwinding polarized signal relay at each end of the line, onewinding of each relay being in a signal circuit including one conductorof the line, a second winding being in a local biasing circuit energizedby the respective current source and a compensating circuit, including athird winding on each relay, extending from the grounded source at oneend over a second line conductor to the grounded source at the otherend, said compensating windings being so arranged and connected in thecircuit as to compensate for effects on the respective relays caused bycurrents flowing in said biasing and signal windings due to a difierencein potential between said grounded sources.

5. In a duplex signaling system, a two-conductor line, a station at eachend thereof, a multiwound polarized relay and a grounded source ofdirect current at each station, a potentiometer in bridge of eachsource, switching means at each station normally connecting groundthrough one winding of the respective relay to one side of the line andthrough a second winding to a predetermined point of the respectivepotentiometer, the potential of said points being equal fractions of thevoltage of the respective sources, said switching means being adapted,when operated, to substitute the respective grounded source for saidground connection and said first and second windings being soproportioned and connected that operation of either means will causeoperation of the distant relay only, a second potentiometer in bridge ofeach source and a connection from the other side of the line at eachstation through a third winding on the respective relay to a point inthe respective second potentiometer which is at the same voltage as thepoint in the first potentiometer thereat, said third windings being soconnected that current flowing therethrough due to a difference inpotential between the two grounded sources will compensate for theeffect in the first and second windings caused by said potentialdifierence.

6. In a duplex signaling system, a two-conductor line, a station at eachend thereof, a multiwound polarized relay and a grounded source ofdirect current at each station, said sources being normally of equalpotential, a normal connection at each station from one side of the lineto ground including one winding of the respective relay, a potentiometerin bridge of each source and of substantially equal resistance, aconnection from the same proportionate point in each potentiometer toground including a second winding of the respective relay, transmittingmeans at each station for simultaneously substituting the respectivegrounded current source, for said ground connection, to both the firstand second windings thereat, a second equal potentiometer in bridge ofeach source, and connections from points therein of the same potentialas the connecting point of the respective first potentiometers to theother side of the line including a third winding of the respectiverelay, said third windings being so arranged and connected that anycurrent change in said first and second windings due to a difference inpotential between said two grounded sources will be neutralized by thecurrent flowing in the third windings.

7. In a duplex signaling system, a two-conductor line, a station at eachend thereof, a multiwinding polarized relay and a grounded source ofdirect current at each station, said sources being normally of equalpotential, a norvrnal connection at each station from one side of theline to ground including one winding of the respective relay, apotentiometer in bridge of each source at each station, a connectionfrom a predetermined point in each potentiometer to ground including asecond winding of the respective relay, transmitting means at each'station for simultaneously connecting the respective current sources inseries with both the first and second relay windings thereat, said relaywindings and current sources being 'so connected that under normal orno-signal conditions each relay will be biased in a non-operatedirection by current flowing in the second winding determined by thepotential of the predetermined point in the respective potentiometer andonly such current will flow in the first winding as may be due to adifference between the ground potentials at the two ends of the line,when signals are being transmitted over the line current will fiow inthe first winding at the transmitting station in a non-operabledirection and in the second winding in an operate direction determinedby the potential of the predetermined point of the potentiometerassociated therewith, which current is insufficient to overcome thenon-operate flux caused by the current in the first winding, and

,at the receiving station current of a certain value continues to flowin a non-operate direction in the second winding thereat determined bythe associate potentiometer connecting point and, of a greater value inthe first winding in an' operate direction to overcome the biasingaction of the second winding current and cause the relay to operate, andwhen both the stations are simultaneously transmitting only such currentwill fiow in the first windings of the two relays as may be due todifferences in the potentials applied at the two ends and both relayswill operate due to the operate direction of the current flowing in thesecond windings and any difierences in earth potential, or in thecurrent sources, at the two ends of the line will be compensated for inboth relays by current determined by these difierences flowing in thethird winding.

GEORGE A. PULLIS.

